There are many variations of membrane valves. Classical microfluidic membrane valves use either a hard-hard seal with very smooth micromachined surfaces, or incorporate a complete additional layer of a soft material between two hard layers. In all cases a good valve seal under practical situations relies on a hard material in contact with a soft material, or a soft material in contact with a soft material. Microfluidic devices are fabricated from polymers for high volume manufacturing, utilize injection moldable materials, and offer the advantage of high levels of integration. One challenge resulting from microfluidic devices fabricated in this way is that the devices are constructed from layers that are finally bonded together. The choice of materials is limited by both the final intended application and available manufacturing techniques. Examples of factors to consider are the application process chemicals and temperatures, and the fabrication processes such as molding and bonding. Satisfying the material requirements of a membrane valve at the same time as all other components that are intended to be part of the monolithic final device, without working with dissimilar materials that are difficult to join, can result in a valve that has a hard membrane pressing against a hard substrate.
The work of Jerman (“Electrically-activated, normally-closed diaphragm valves”, J. Micromachining and Micrengineering, V4, 1994 pp 210-216), describes a silicon-on-silicon micromachined valve. Smooth surfaces resulted in leakage rates (on:off flow rates) of 5000:1.
The work of Bruns (Silicon Micromachining and High-speed gas chromatography, Proceedings of the 1992 International Conference on Industrial Electronics, Control, Instrumentation and Automation, 1992, V3, pp 1640-1644) describes a trapped polymer membrane between a glass membrane and a silicon valve body, to replace the hard-hard valve seal with a hard-soft valve seal.
The recent work of Chen et al (Floating-Disk Parylene Microvalves for Self-Pressure-Regulating Flow Controls, Journal Of Microelectromechanical Systems, Vol. 17, No. 6, December 2008), describes a silicon and parylene valve structure that consists of a floating parylene disc. The work in the paper aims to produce a passive valve with self-regulating behavior resulting from the movement of the floating parylene disc.
There is thus a need for a microvalve having a simple design which provides ease of manufacture and satisfactory performance. More specifically, there is therefore a need for a microvalve formed from bonding similar materials together for the fabrication of the microvalve, while simultaneously introducing a soft layer for valve sealing.